1. Technical Field
This invention relates to procedures for developing a resultant force based spot weld failure criterion for predicting multi-axial loaded spot weld failure.
2. Discussion of Prior Art
Spot welding is widely used in joining sheet metal members in the manufacture of automotive bodies because such welding can be extremely fast. Spot welding is the simplest form of resistance welding in which electrodes apply some pressure when squeezingly contacting the sheet metal assembly while low voltage current, accompanied by sufficient amperage, is passed between the electrodes to locally raise the sheet metal to a melting and welding temperature.
The strength and stiffness of the spot weld joints can vary considerably depending on the direction, complexity and cyclic nature of the joint loading. The unreliability of current methods to predict the failure mode of a specific spot welded joint in automotive bodies has misled designers to inaccurately design spot weld structures out of an abundance of precaution. With the imposition of stricter fuel economy standards for automotive vehicles, the spot weld body structures have come under severe scrutiny to allow for weight reduction.
Existing structural analysis techniques for spot welded structures consider only two types of loadings or failure modes at any one time that may act on a structure; such method lacks the increased accuracy and reliability that will assist in structural safety and weight reduction without jeopardizing risk of failure over the useful life of the structure. Often, different failure modes act on the welded structure at the same time, including a variety of modes selected from shear tension, in-plane rotation, coach-peel, and normal or pull tension. These failure modes need to be considered not only by themselves, but in combination for predicting accurate conditions for combined failure of the spot welded structure.